Solid tissue tumors, such as those found in the liver, traditionally have been treated with systematic chemotherapy, surgical resection, or local radiation therapy. Many tumors, however, remain poorly responsive to these therapeutic modalities and necessitate the use of alternative treatments, such as thermal ablation of the tumor. Thermal sources for these treatment modalities include high-intensity ultrasound, laser, microwave, and radiofrequency (RF) energy. Of these different types of ablation techniques, RF ablation has proven to be safe, predictable, and inexpensive, and has emerged as the thermal ablation modality that most easily creates large volumes of tissue necrosis.
Although RF ablation of the tumor can be implemented during open surgery, it is most often performed percutaneously. One RF ablation technique utilizes a single needle electrode or a multiple needle electrode array that is inserted percutaneously using a surgical probe and guided with real-time ultrasound, computed tomography (CT) scan or magnetic resonance imaging (MRI) into the tumor. One properly positioned, the needle electrode is activated, and alternating current is transferred from the needle electrode into the surrounding tissue, causing ionic agitation of the surrounding cells, ultimately leading to the production of frictional heat. As tissue temperatures increase between 60-100° C., there is an instantaneous induction of irreversible cellular damage referred to as coagulation necrosis. The treatment area is monitored ultrasonographically for increased echogenicity during the procedure, which corresponds to the formation of tissue and water vapor microbubbles from the heated tissue and is used to roughly estimate the boundaries of the treatment sphere.
Often, when performing a RF ablation procedure, the presence of blood vessels within or near the tumor causes the conduction of thermal energy away from the target tissue and into the relatively cooler blood. This may cause irregular shaped ablation regions, or sometimes even prevent ablation. When such procedures are performed using open surgical procedures, a surgeon may typically clamp the respective blood vessel, e.g., by using his or her fingers or by using a pair of forceps, thereby reducing or eliminating the blood flow adjacent or through the ablation site. For example, if the tumor is within the liver, the portal vein and/or hepatic artery at the porta hepatis may be clamped. This technique is called a “Pringle maneuver.”
When a percutaneous ablation procedure is performed, however, a Pringle maneuver may not be possible, due to the lack of direct access to the vessel and/or the distance from the abdominal wall to the vessel. Angiographic portal arterial, or major vessel balloon occlusion has been used to prevent or minimize blood flow through the ablation site. This technique, however, is not flexible in that the human vasculature often prevents or makes difficult the introduction of the balloon into certain blood vessels, e.g., the portal vein in the liver.
Accordingly, apparatus and methods for occluding vessels in connection with an organ being treated by an RF ablation or other hyperthermic procedures would be useful.